28 Marine Invertebrates 



of seawater salts remains more or less uniform throughout the entire 

 expanse of the ocean, varying only in concentration. This may be seen 

 from Table 2 (quoted from Quinton, 1912) representing the results of the 

 analyses of Forchhammer (1865), Makin (1878), and Dittmar (1884), 

 and expressed as percentage of total solids. 



table 2. Composition of seawater (percentage of total solids). 



Forchhammer Makin Dittmar 



NaCl 78-32 76-9IS 77-758 



MgCb 9-44 11 -4°7 10.878 



MgS0 4 6.40 4.483 4-323 



CaS04 3.94 4-226 4.070 



K2SO4 2.468 2.465 



KC1 1.69 



MgC0 3 0.290 



MgBr2 0.298 0.217 



Other 0.21 0.206 



Analytical and physiological work carried out during the last two 

 decades has greatly increased our knowledge of the chemistry of sea- 

 water, and has shown that certain substances, such as phosphates, 

 nitrates, silica, and iron, which occur in infinitesimally small amounts, 

 are indispensable to the growth and propagation of marine forms. A 

 complex interrelationship between the concentration of the nutrient 

 salts and the productivity of the sea is at present the principal problem 

 of oceanic biology. Progress in this field of research became possible 

 only after the chemists developed and perfected simple colorometric 

 methods of determination of phosphates, nitrates, iron, and silica.* 



According to Thompson and Robinson (1932) the following elements 

 or their compounds (written in the order of their abundance) are deter- 

 minable in seawater. 



table 3. Approximate composition of seawater with a 

 chlorinity of 19.00%. 



Concentration as millimols Concentration as millimols 



or milligram atoms per or milligram atoms per 



Constituent kg. of seawater Constituent kg. of seawater 



Chlorine 535-0 Bromine 0.81 



Sodium 454-0 Strontium 0.15 



Sulphate 82.88 Aluminum 0.07 ? 



Magnesium 52 .29 Fluorine 0.043 



Calcium 10.19 Silicon 0.04 



Potassium 9-6 Boron 0.037 



Carbon Dioxide 2.25 Lithium 0.015 



*The description of these methods would be out of place in the present book and the 

 readers interested in these are referred to the book of Harvey (1928) and original papers 

 published in the Journal of the Marine Biological Association of Plymouth and other 

 oceanographical periodicals. 



